The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Attaching composite structures to other components or structures can be challenging. Composite structures, such as carbon fibre components, are generally extremely stiff in the fibre direction, but can have less strength perpendicular to the fibre direction. Attachment holes for a bolted joint connection are generally formed perpendicular to the fibre direction. Compressive loads through a joint formed through such attachment holes will therefore be perpendicular to the fibres rather than aligned with them. The stiffness of the material perpendicular to the fibres is quite low. Consequently, a low clamping pressure is required between the head of a bolt/washer and a mount to which it is to be connected to avoid damage. High clamping pressures can damage composite material at or immediately adjacent a preformed attachment hole, causing delamination at or immediately adjacent the edge of that attachment hole. This makes it difficult to achieve a stiff joint with conventional attachment and fastening arrangements.
A washer may be used to distribute the load over a greater area. However, conventional flat washers provide an uneven load distribution about the attachment aperture. In most cases, the load is greater in the region closer to the head of the bolt, thus creating an undesirable high compression zone close to the edge of the attachment hole.
Special fastener combinations may therefore be used for composite structures. However, most prior bolt-nut combinations include geometries which effect a loading of composite structures at or immediately adjacent an attachment hole in which they are used, and therefore contribute to a weakening, breakdown or destruction of the composite material in this area.
It would therefore be desirable to provide an attachment arrangement for a composite wheel that overcomes one or more of the above limitations.